Reciprocating hermetic compressor

ABSTRACT

A reciprocating hermetic compressor, of the type including a rotor with permanent magnets and having its tubular vertical shaft ( 5 ) provided radially externally to the internal surface thereof with at least one axial channel ( 10 ) of oil conduction, having a lower end ( 11 ) immersed in the lubricant oil being pumped from a lubricant oil sump ( 2 ) defined at the bottom of the hermetic shell of the compressor, and an upper end ( 12 ) opened to a median radial duct ( 5   a ), which conducts lubricant oil to the parts of the compressor spaced away from the lubricant oil sump ( 2 ).

FIELD OF THE INVENTION

The present invention refers to a construction for a reciprocatinghermetic compressor of the type having a motor with permanent magnetsaffixed to a vertical shaft and, more particularly, to a constructionfor this vertical shaft of the reciprocating compressor.

BACKGROUND OF THE INVENTION

Compressors having an electric motor with a rotor carrying permanentmagnets are used in refrigeration appliances because they allow theangular speed of the compressor shaft to be varied, either continuouslyor discretely, within a determined rotation range.

The hermetic refrigeration compressors are constructed according to twopossible dispositions of the mechanical elements inside the shellthereof. In one of these constructions, the connecting rod-crankshaftsystem of the compressor is positioned below the electric motor, closeto or immersed in the lubricant oil sump existing at the bottom of thecompressor shell. In another of these constructions, the connectingrod-crankshaft system is positioned above the electric motor andtherefore spaced, by a considerable height, from the lubricant oil sumpprovided at the bottom of the compressor shell.

Among other factors, the lubrication efficiency of the mechanical systemis affected by the amount of oil reaching the movable parts, resultingfrom the rotation of the compressor shaft, which actuates an oil pump(or centrifugation tube). The oil pumping resulting from the rotation ofthe tubular vertical shaft generates an oil transportation ascendingcurve, in the form of an oil parabola, whose upper end should reach orsurpass an oil delivery point in the form of a median radial ductprovided in the body of the tubular vertical shaft of the compressor ina median Portion of its longitudinal extension.

Thus, the amount of oil available for lubricating the movable partsdepends on the centrifugation speed which, on its turn, is equal to theangular speed of the shaft. If the angular speed of the shaft is lowerthan a predetermined limit value, the end of the parabola will not reachthe delivery point, and therefore there will not be enough pumped oilfor lubrication. The amount of pumped oil also depends on the requiredelevation height, which is the height defined between the oil level inthe sump and the outlet of said oil at the delivery point.

In order to guarantee an efficient lubrication of the movable partsduring the operation of the compressor in low rotations, some knowntechniques are used.

One of the techniques to guarantee the volume of oil needed to lubricatethe movable parts of the compressor is to use a type of constructionwhich foresees the connecting rod-crankshaft system situated below theelectric motor. In this case, there is a considerable reduction in thepumping elevation, which is necessary between the oil level in the sumpand the delivery point of the lubricant oil (which, in this case, may bethe connecting rod-crankshaft system itself).

Another technique for reducing the height between the oil level and thedelivery point of the lubricant oil (elevation height) is to add oil tothe sump, as a form of increasing its level and, consequently, reducethe elevation height to be overcome.

The lubrication of the movable parts can also be assured by limiting theminimum rotation in which the shaft is operated, in order to assure thata minimum indispensable amount of oil always reaches the desired height.

Using the type of construction in which the mechanical system ispositioned below the compressor shell (motor at the upper part) has thedisadvantage that the coils of the electric motor do not have a directcontact with the oil in the sump (immersion) and, therefore, the coolingof said coils is less efficient. The poor cooling of the motor may causedegradation of its insulating and conducting materials. Anotherdisadvantage of this technique is that the mechanical system may cause,by the movement of the shaft, a turbulence of the oil in the sump, whichmay generate noise during operation.

A deficiency in using the technique of increasing the oil level in thecompressor sump is the higher cost of adding more oil. Anotherdisadvantage of increasing the oil level is associated with thepossibility of this oil contacting the lower surface of the rotor duringthe compressor operation, producing whirl and foaming of the lubricantoil. This foaming causes deficiency in the lubrication and increases thepower consumption for the compressor operation.

The technique of limiting the minimum rotation in which the shaftoperates, in order to guarantee that a minimum indispensable oil amountalways reaches a desired height has, as an intrinsic disadvantage, thelimitation of the rotation range in which the compressor may operate.

DISCLOSURE OF THE INVENTION

Thus, it is an objective of the present invention to provide areciprocating hermetic compressor in which, independently from thepositioning of its motor assembly inside the shell, occurs an adequatelubrication of the movable parts of the compressor needing lubrication,even in low rotations and with no need for increasing the oil level inthe sump defined at the bottom of the compressor shell, or for usingadditional parts other than those already existing in the pumping systemof said compressor.

This and other objectives are attained by a reciprocating hermeticcompressor, including a hermetic shell, which defines at its bottom alubricant oil sump and which lodges a cylinder block supporting atubular vertical shaft having at least a median radial duct of oilpassage and carrying at the bottom thereof an oil pump immersed in thelubricant sump, the oil being pumped upon rotation of the tubularvertical shaft towards the median radial duct, said tubular verticalshaft being provided, axially and externally to its internal periphery,with at least one axial channel of oil conduction, having a lower endimmersed in the lubricant oil being pumped and an upper end opened to arespective median radial duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the attacheddrawings, in which:

FIG. 1 shows, schematically and in a longitudinal sectional view, partof a reciprocating compressor, with a tubular vertical shaft mounted toa cylinder block and carrying an oil pump, constructed according to theprior art;

FIG. 2 shows, schematically and in a longitudinal sectional view, partof the tubular vertical shaft of the compressor constructed according tothe present invention; and

FIG. 3 shows, schematically and in a cross-sectional view, the tubularvertical shaft of the compressor constructed according to the presentinvention.

FIG. 4 is a cross-sectional view of a part of the shaft showing thechannel; and

FIG. 5 is a cross-section along line 5—5 of FIG. 4.

BEST MODE OF CARRYING OUT THE INVENTION

According to FIG. 1, a hermetic compressor of vertical shaft comprises ahermetic shell 1 defining a lubricant oil sump 2 at the bottom thereofand lodging therewithin: a cylinder block 3 incorporating a bearing 4,for supporting the tubular vertical shaft 5, to which is mounted, at aportion of said shaft below the bearing 4, an electric motor rotor 6carrying magnets 7, and further including a stator 8 affixed to thecylinder block 3.

The tubular vertical shaft 5 carries, at the lower portion thereof, anoil pump 9, whose lower end is immersed in the oil mass provided in thelubricant oil sump 2. During rotation of the tubular vertical shaft 5,the oil of the lubricant oil sump 2 is upwardly conducted bycentrifugation, through an oil duct defined inside the tubular verticalshaft 5, to a median radial duct 5 a provided in the body of the tubularvertical shaft 5 at the region of the bearing 4 through the lateral wallof said tubular vertical shaft 5. The lubricant oil, which is pumped bythe oil pump 9 upon rotation of the rotor 6 and tubular vertical shaft 5and which reaches the median radial duct 5 a is distributed to themovable parts of the compressor spaced away from the lubricant oil sump2 of said compressor.

In these compressors, the pumping efficiency is a function of therelationship between a smaller diameter of the lower end of the oil pump9 immersed in the lubricant oil sump 2, and a larger diameter defined bythe internal diameter of the tubular vertical shaft 5. The closer thesevalues, lesser will be the lubrication efficiency of the oil pump, asalready discussed in the beginning of this disclosure. According to thepresent invention, the improvement of the pumping capacity is obtainedby increasing the difference between the smallest radius of oiladmission defined at the lower end of the oil pump 9, and a largerradius of maximum value in relation to the oil pump axis. This largerradius is achieved by machining at least one axial channel 10 of oilconduction, disposed radially externally to an internal lateral surfaceof the tubular vertical shaft 5 and having at least part of thelongitudinal extension thereof substantially rectilinear and extendingalong a determined longitudinal extension of said tubular vertical shaft5, and communicating a lower nozzle 9 a, of oil admission to the oilpump 9, with the median radial duct 5 a.

With this radius increase, the oil pumping to the height where is foundthe median radial duct 5 a may occur with a lower rotation of the motor.This allows the compressor to operate with lower rotations than thoseconventionally required to the same oil pumping to said median radialduct 5 a.

The oil pumping resulting from the rotation of the tubular verticalshaft 5 determines a curve of oil distribution in the form of aparaboloid generated by centrifugation and whose height is proportionalto the square of the smallest radius of centrifugation found in the pathfrom the oil level in the sump up to the median radial duct 5 a.

According to the present invention, each axial channel 10 has at least asubstantial part of its longitudinal extension disposed between a lowerend 11 immersed in the oil being pumped by the oil pump 9 when underoperation, and an upper end 12 opened to a respective median radial duct5 a.

The lower end 11 is provided in the tubular vertical shaft 5 opened tothe inside of the oil pump 9, particularly to the lower end of thetubular vertical shaft 5, which is found immersed in the lubricant oilduring rotation of the tubular vertical shaft 5.

In the preferred illustrated solution (FIGS. 2 and 3), the tubularvertical shaft 5 is provided with a single axial channel 10, for exampleupwardly diverging from the axis of the tubular vertical shaft 5 fromthe lower end 11 thereof and which is produced in the form of ahalf-tubular cross-section from the internal lateral surface of thetubular vertical shaft 5. Depending on the inclination, the groove whichdefines the axial channel 10 has a variable increasing depth from thelower end 11 of said axial channel 10. With the provision of an axialchannel 10 which produces, at the region of the tubular vertical shaft5, an increase in the inner radius thereof, the oil distribution curvehas a height which is sufficient to reach the median radial duct 5 a,even in low rotations.

The radius increase may also be obtained from axial slots producedradially externally to the internal lateral surface of the tubularvertical shaft 5, in the wall thickness and along the longitudinalextension thereof, parallel to its axis or also diverging therefrom andwith a cross-section different from the one described herein, withoutaltering the efficiency of oil conduction.

The present solution has the advantages of increasing the inner radiusof centrifugation and, consequently, the lubrication efficiency, even inlow rotations of the motor, without requiring additional parts orconstructive modifications of the oil pump.

What is claimed is:
 1. A reciprocating hermetic compressor comprising: ahermetic shell which defines at its bottom a sump for oil lubricant; acylinder block within said hermetic shell supporting a tubular verticalshaft that is rotated, said tubular shaft having at least one axialchannel on its internal surface extending upwardly from the tubularshaft lower end and a radial duct through the shaft above the tubularshaft lower end that communicates with said at least one axial channel;the lower end of said tubular shaft being immersed in the oil in saidsump to be pumped upwardly along a said at least one axial channel andout through said radial duct to other parts of the compressor as saidshaft is rotated.
 2. A reciprocating hermetic compressor, as in claim 1wherein a said at least one axial channel has at least a substantialpart of its longitudinal extension inclined and upwardly diverging fromthe axis of the tubular vertical shaft.
 3. A reciprocating hermeticcompressor, as in claim 2, wherein each axial channel is in the form ofa longitudinal groove provided in the internal lateral surface of thetubular vertical shaft.
 4. A reciprocating hermetic compressor, as inclaim 3, wherein each axial channel has a half-tubular cross-section. 5.A reciprocating hermetic compressor, as in claim 4, wherein each axialchannel has a variable cross-section along the longitudinal extensionthereof.
 6. A reciprocating hermetic compressor as in claim 1 furthercomprising a pump at the lower end of the shaft to pump oil from thesump.